Davies Sarah W, Moreland Kelsey N, Wham Drew C, Kanke Matt R, Matz Mikhail V
Department of Biology, Boston University, Boston, MA, USA.
Department of Integrative Biology, The University of Texas at Austin, Austin, TX, USA.
Mol Ecol. 2020 Dec;29(23):4559-4572. doi: 10.1111/mec.15668. Epub 2020 Oct 31.
Many broadly-dispersing corals acquire their algal symbionts (Symbiodiniaceae) "horizontally" from their environment upon recruitment. Horizontal transmission could promote coral fitness across diverse environments provided that corals can associate with divergent algae across their range and that these symbionts exhibit reduced dispersal potential. Here we quantified community divergence of Cladocopium algal symbionts in two coral host species (Acropora hyacinthus, Acropora digitifera) across two spatial scales (reefs on the same island, and between islands) across the Micronesian archipelago using microsatellites. We find that both hosts associated with a variety of multilocus genotypes (MLG) within two genetically distinct Cladocopium lineages (C40, C21), confirming that Acropora coral hosts associate with a range of Cladocopium symbionts across this region. Both C40 and C21 included multiple asexual lineages bearing identical MLGs, many of which spanned host species, reef sites within islands, and even different islands. Both C40 and C21 exhibited moderate host specialization and divergence across islands. In addition, within every island, algal symbiont communities were significantly clustered by both host species and reef site, highlighting that coral-associated Cladocopium communities are structured across small spatial scales and within hosts on the same reef. This is in stark contrast to their coral hosts, which never exhibited significant genetic divergence between reefs on the same island. These results support the view that horizontal transmission could improve local fitness for broadly dispersing Acropora coral species.
许多广泛分布的珊瑚在定居时从其环境中“水平”获取它们的藻类共生体（共生藻科）。如果珊瑚能够在其分布范围内与不同的藻类建立联系，并且这些共生体的扩散潜力降低，那么水平传播可以提高珊瑚在不同环境中的适应性。在这里，我们使用微卫星量化了密克罗尼西亚群岛两个空间尺度（同一岛屿上的珊瑚礁以及岛屿之间）上两种珊瑚宿主物种（风信子鹿角珊瑚、指状鹿角珊瑚）中枝管藻属藻类共生体的群落差异。我们发现，这两种宿主都与两个遗传上不同的枝管藻属谱系（C40、C21）内的多种多位点基因型（MLG）相关联，这证实了鹿角珊瑚宿主在该区域与一系列枝管藻属共生体相关联。C40和C21都包括多个具有相同MLG的无性系谱系，其中许多跨越宿主物种、岛屿内的珊瑚礁地点，甚至不同的岛屿。C40和C21在岛屿间都表现出适度的宿主特异性和分化。此外，在每个岛屿内，藻类共生体群落都按宿主物种和珊瑚礁地点显著聚类，这突出表明与珊瑚相关的枝管藻属群落是在小空间尺度上以及同一珊瑚礁上的宿主内形成结构的。这与其珊瑚宿主形成了鲜明对比，珊瑚宿主在同一岛屿上的珊瑚礁之间从未表现出显著的遗传分化。这些结果支持了水平传播可以提高广泛分布的鹿角珊瑚物种的局部适应性这一观点。
